1. Field of the Invention
The present invention relates to an improved coaxial RF probe for testing or trouble-shooting microstrip circuits while avoiding the need for adding conventional coupled test ports or resistive network test ports, which test ports degrade the performance of microstrip circuits, require space and increase the cost and weight of the circuit board.
2. Discussion of the State of the Art
Manufacture and maintenance of a microstrip circuit require that functionality of various stages of the circuit be measurable. In RF circuitry it is conventional to incorporate coupled test ports on resistive network test ports at predetermined critical locations along the microstrip circuit in order to test, measure or trouble-shoot the performance of the circuit at these specific locations.
Such test ports have several disadvantages including being localized, expensive, requiring space and adding weight to the circuit board. More importantly, such test ports degrade the operation or performance of the circuit even when no tests are being performed.
It is also known to test the operation or performance of a microstrip circuit by means of a coaxial RF probe or sniffer probe having a central circuit contact and an outer coaxial jacket contact having a flexible ground wire designed to be clipped to a ground plane area spaced from the microstrip circuit. A DC-blocking device is associated with the central contact in order to provide a contact which protects the sensitive measurement device, such as a spectrum analyzer, power meter or other similar instrument against direct current damage.
While such conventional coaxial RF probes enable testing at any point along a microstrip circuit and avoid the need for test ports on the microstrip circuit, they do not have a reliable grounding system or provide a fixed-distance ground point and therefore their performance is erratic and unreliable. Any coaxial RF probe exhibits high electrical losses, and such losses are unpredictable and variable when the spacing between the microstrip contact and the ground contact is varied.